The present invention relates to a molding die drive unit for advancing and retracting at least a part of a die to change a volume of a cavity provided in the die for compressing or expanding (enlarging volume) a resin in the die during injection molding, injection compression molding, press molding, large blow gas-injection molding, multi-layered molding, foam molding thereof, and expansion molding of glass-fiber containing resin; a molding unit incorporating the molding die drive unit; and a molding method using the molding unit.
In injection compression molding, molten resin is loaded inside a die closed with a predetermined compression margin retained and, subsequently, a compression force is applied to the molten resin filled in the die by clamping the die for rendering shape.
According to the injection compression molding, since the molding process can be conducted by a low resin injection pressure and in-mold pressure can be made uniform, warp and distortion are not caused to the molding product, thus being capable of obtaining molding products having good shape even with small thickness and causing less damage to a surface member during surface member integrating molding.
A molding machine used for the injection compression molding generally has a clamp unit for advancing a movable die provided to the molding machine movably toward a stationary die fixed to the molding machine, and a compression unit for compressing the molten resin filled inside the die.
As shown in Japanese Patent Publication Laid-Open No. Sho 57-95429 and Japanese Patent Publication Laid-Open No. Sho 60-122128, a conventional compression unit has a movable portion for increasing and decreasing a volume of a die cavity inside the die and a pin abutted to the movable portion through which the movable portion is advanced to reduce the volume of the cavity so that the molten resin filled inside the die is compressed.
For advancing the movable portion, a pair of slant member having mutually touching slant surfaces slanting relative to advancing direction of the movable portion is disposed along an advancing direction thereof and one of the slant members is moved in a direction orthogonal with the advancing direction of the movable portion to generate compression force.
Since injection compression molding is impossible for an ordinary die having no movable portion thereinside, such compression unit lacks general-purpose properties.
In order to solve the above problems, the Applicant of the present application has proposed a compression unit 75 having unitized mechanism for pressing a movable die 71 toward a stationary die 72 being capable of attaching and detaching between the movable die 71 and a clamp unit 74 (Japanese Patent Publication Laid-Open No. Hei 7-164500).
The compression unit 75 has a pair of slant member 77 and 78 disposed along the compressing direction both having a slant surface 76 slanting toward compressing direction. In the slant members, the slant member 78 on the clamp unit 74 side is advanced toward the slant member 77 by a cylinder unit 79 to generate compression force.
According to the compression unit 75, the entire thickness can be made relatively small as compared to the unit described in the Japanese Patent Publication Laid-Open No. Sho 57-95429 etc., which can be attached to an ordinary injection molding machine together with the die, thereby enabling injection compression molding even with an ordinary die having no movable portion installed therein so that general purpose properties of the molding machine can be improved.
However, since the above compression unit 75 converts drive force direction of the cylinder unit 79 by slidably moving the slant surfaces 76 of the relatively moving slant members 77 and 78, friction loss is increased, which result in low mechanical efficiency (50 to 70%) of the unit.
Further, in a molding method accompanying retraction of the movable die during molding process such as the foam molding which requires foaming of foaming agent by enlarging the volume of the cavity during injection or after injection, since the slide resistance of the slant members 77 and 78 is increased by the pressure of the resin injected into the die and since frictional force between the slant members 77 and 78 is static friction, large strength is required for initiating retraction of the slant member 78 for resisting against the static friction.
On the other hand, when the slant member starts moving, the frictional force between the slant members 77 and 78 changes from the static friction into dynamic friction and the slide resistance rapidly decreases.
Accordingly, moving speed is not stabilized and smooth relative movement of the slant members 77 and 78 is difficult, so that minute adjustment of the moving speed and position of the movable die are impossible, proving not suitable for molding method accompanying retraction of the movable die during molding process.
Further, since the pair of the slant members 77 and 78 are linearly disposed along the compressing direction, there is natural limit for reducing the thickness of the compressing unit.
An object of the present invention is to provide a molding die drive unit being capable of compressing and expanding the molten resin injected into the die and having reduced thickness and superior mechanical efficiency, a molding unit installed with the molding die drive unit and molding method using the molding unit.
The present invention is a unitized die driving unit detachably attached to any one of the stationary die and the movable die that intends to achieve the above object by providing a main cylinder used for pressurization and a plurality of sub cylinder unit used for pressurization and high-speed movement around the main cylinder unit.
More specifically, a molding die drive unit according to the present invention is for forming a cavity between a stationary die and a movable die for molten resin to be loaded, the molding die drive unit being detachably attached to either the stationary die or the movable die for moving a part of or entirety of at least one of the stationary die and the movable die to be advanced and retracted relative to the cavity. The molding die drive unit is characterized in having: a large-diameter main cylinder unit; and a plurality of small-diameter sub cylinder unit disposed around the main cylinder unit being spaced apart with each other.
In the present invention, the molding die drive unit advances and retracts a part of entirety of the stationary die or the movable die, or, a part of the stationary die or the movable die relative to the cavity. Advancement or retraction of the part of the stationary die or the movable die refers to advancement and retraction of a slide die when the dies are constructed of die body and the slide die disposed slidably relative to the die body.
According to the present invention, the molten resin is injected into the cavity after closing the stationary die and the movable die. After a predetermined time after initiating injection of the molten resin, the main cylinder unit and the sub cylinder unit are driven to advance and retract at least a part of the stationary die and the movable die relative to the cavity to compress or expand (volume enlargement) the molten resin in the cavity for rendering shape.
Small-diameter sub cylinder unit is used for advancing and retracting at least a part of the stationary die or the movable die to a predetermined position. In other words, hydraulic fluid (hydraulic pressure) is supplied from an external hydraulic source to the sub cylinder. At this time, by allowing circulation of the hydraulic fluid to the main cylinder unit, the main cylinder unit advances and retracts in accordance with advancement and retraction of the sub cylinder unit.
On the other hand, for pressurizing the molten resin in the cavity, not only the sub cylinder unit is advanced but also the large-diameter main cylinder unit is advanced by supplying hydraulic fluid (hydraulic pressure) thereto. At this time, since the circulation of the hydraulic fluid to the main cylinder is blocked, the hydraulic fluid (hydraulic pressure) to the main cylinder unit does not escape, thereby securely conducting advancement of the main cylinder unit.
Accordingly, in the present invention, the injection compression molding is possible by advancing at least a part of the stationary die or the movable die after initiating the injection of the molten resin into the cavity, and injection expansion molding and injection compression expansion molding is possible by advancing and retracting a part of the stationary die or the movable die.
Furthermore, since the large-diameter main cylinder unit is mainly used for pressurizing the molten resin, uniformity of strength applied to the entire molten resin can be secured, thereby securing parallelization between the movable die and the stationary die.
Further, since the large-diameter main cylinder unit is advanced only in pressurizing the molten resin and only the small-diameter sub cylinder unit is driven in retracting at least a part of the stationary die or the movable die, operation circuit for retracting the main cylinder unit is not necessary.
In other words, since the main cylinder unit becomes a single-drive cylinder only for advancement and retraction is conducted by the small-diameter sub cylinder unit, the cylinder units can be constructed of thin unit having large mechanical output, which can be attached to an ordinary injection molding machine together with the die.
In the above, the main cylinder unit may preferably be connected to a main cylinder driving mechanism, the main cylinder driving mechanism having: a main cylinder flow channel disposed between a hydraulic fluid feeder for feeding hydraulic fluid in a hydraulic tank and the main cylinder unit; and a main cylinder switching valve provided to the main cylinder flow channel for switching position thereof between a position for supplying the hydraulic fluid to the main cylinder unit to advance the main cylinder unit and a position for blocking supply of the hydraulic fluid to the main cylinder unit and for returning the hydraulic fluid in the main cylinder unit to the hydraulic tank.
According to the above arrangement, the circulation of the hydraulic fluid between the main cylinder unit and the hydraulic tank can be easily allowed and blocked by the main cylinder switching valve.
The molding die drive unit may further include a reserve tank disposed adjacent to the main cylinder unit and an on-off valve provided between the main cylinder unit and the reserve tank for allowing or blocking circulation of the hydraulic fluid between the main cylinder unit and the reserve tank.
In other words, the reserve tank may be intercommunicated with the main cylinder unit through the on-off valve.
According to the above arrangement, when the main cylinder unit advances and retracts in accordance with advancement and retraction of the sub cylinder unit, the exclusive reserve tank is used for supplying the main cylinder unit with hydraulic fluid and returning the hydraulic fluid from the main cylinder unit.
The reserve tank in communication with the main cylinder unit may be disposed adjacent to the main cylinder unit.
According to the above arrangement, the hydraulic fluid circulates smoothly between the reserve tank and the main cylinder unit when at least a part of the stationary die and the movable die advances and retracts at a high speed so that responsivity of the die movement can be improved and the size of the external hydraulic tank and the hydraulic pump can be reduced.
According to the present invention, the sub cylinder unit may be connected to a sub cylinder driving mechanism, the sub cylinder driving mechanism having: a sub cylinder flow channel provided between the hydraulic fluid feeder and the sub cylinder unit; a sub cylinder switching valve provided to the sub cylinder flow channel for switching a position thereof among a position for supplying the hydraulic fluid to the sub cylinder unit to advance the sub cylinder unit, a position for supplying the hydraulic fluid to the sub cylinder unit to retract the sub cylinder unit and a position for blocking intercommunication of the hydraulic fluid between the sub cylinder unit and the hydraulic fluid feeder.
According to the above arrangement, since the sub cylinder unit can easily be advanced and retracted by switching the sub cylinder switching valve, the molding process can be rapidly conducted.
Further, an opening may be formed along axis center of the main cylinder unit.
According to the above arrangement, the resin injection nozzle can be inserted from the opening, so that disposition on the stationary die side is possible. And when attached to the movable die side, the ejector rod can be inserted thereto, thereby facilitating ejection of molding products.
A molding unit according to the present invention has the above molding die drive unit between a movable platen having the movable die thereon and a stationary platen having the stationary die thereon or, alternatively, the molding die drive unit may be attached to the movable platen or the stationary platen. Further, a pressure-receiving block may be provided between the movable platen and the stationary platen.
According to the molding unit having the pressure-receiving block provided to the movable platen and the stationary platen, the pressure-receiving block provided to the stationary platen abuts to the pressure-receiving block provided to the movable platen in advancing the movable platen to receive high-pressure clamping force. The pressure-receiving blocks secure parallelization between the stationary die and the movable die attached to the platens, thereby conducting appropriate injection operation. Incidentally, the pressure-receiving block is important for increasing and decreasing the cavity volume by advancing and retracting the entire movable die.
A molding method for molding resin according to the present invention is a molding method using the above molding unit, which is characterized in having the steps of: injecting a molten resin to the cavity; and advancing and retracting a part or an entirety of at least one of the stationary die and the movable die relative to the cavity at any time period after initiation of injection.
In the above molding method, the sub cylinder unit may be driven to advance the part or the entirety of at least one of the stationary die or the movable die at a high speed relative to the cavity while intercommunicating the main cylinder unit with the hydraulic tank or the reserve tank, and, subsequently, hydraulic pressure may be applied to both of the main cylinder unit and the sub cylinder unit while blocking intercommunication of the main cylinder unit with the hydraulic tank or the reserve tank to pressurize the molten resin loaded in the cavity to advance the part or the entirety of at least one of the stationary die or the movable die relative to the cavity.
According to the above arrangement, injection compression molding can be appropriately conducted.